1. Field of the Invention
The present invention relates to an electric cell which utilizes a polyaniline as a positive electrode active material, lithium or a lithium alloy as a negative electrode active material, and a non-aqueous electrolyte as an electrolyte.
2. Description of the Prior Art
Electric cells comprising lithium as a negative electrode active material have hitherto been known to be those having high energy densities and high discharge voltages. In such cells, non-aqueous electrolytes, such as non-aqueous electrolytic solutions containing an electrolyte dissolved in a non-aqueous solvent, have usually been utilized as electrolytes in order to stabilize their cell performance under the conditions of high energy densities and high discharge voltages.
Recently, electric cells utilizing organic polymeric materials have been developed for the purpose of miniaturizing cells, reducing their weights and/or improving their flexibility. In particular, there have been a great number of attempts to apply organic electroconductive polymeric materials such as polyanilines to electric cells as electrode active materials. When polyanilines are utilized as electrode active materials of electric cells, those having excellent cell performance can be obtained: that is, secondary cells comprising polyanilines may have larger charge and discharge capacities and better cycle life as compared with those utilizing other organic electroconductive polymeric materials. Accordingly, polyanilines among organic electroconductive polymeric materials are expected to be most promising electrode active materials for practical use in electric cells.
Thus, it has been expected that high performance electric cells with good functions can be obtained if polyanilines are utilized as positive electrode active materials of electric cells a which comprise lithium as negative electrode active materials a and non-aqueous electrolytes.
However, electric cells utilizing polyanilines as electrode active materials have not become practical due to the reasons that such cells have higher internal resistance and shorter cycle life as compared to electric cells using conventional inorganic materials as electrode active materials. Particularly, such disadvantages will be more serious if polyanilines are utilized as positive electrode active materials in secondary lithium cells having high energy densities and high discharge voltages.
Such secondary lithium cells may be described in more detail: Li secondary cells can be charged and discharged repeatedly, have excellent cell performance such as a high energy density and a discharge potential, and are able to be miniaturized and reduced in their weight. Therefore, attempts to apply such secondary Li cells to various uses have been greatly achieved.
On the other hand, a demand for secondary cells which are small in size and can endure 1,000 to 2,000 cycles of charge and discharge at discharge capacity of at least 1 mAH, as secondary cells for memory backup of personal computer ICs, has been increasing as personal computers and game instruments using such computers have become routine.
In order to attain good durability upon use over a longer period and/or more repeated cycles of charge and discharge, there are attempts made to prevent the formation of lithium dendrite during the charge and discharge cycles by utilizing a lithium alloy such as LiAl instead of lithium as a negative electrode active material of a secondary cell. However, such excellent durability upon repeated charge and discharge cycles has not been attained yet.